Chapter 3—Affected Environment
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Final EIS Chapter 3—Introduction CHAPTER 3—AFFECTED ENVIRONMENT 3.1 INTRODUCTION The Pinedale planning area is composed of approximately 922,880 acres of Bureau of Land Management (BLM)-administered public land surface and 1,199,280 acres of federal mineral estate in portions of Sublette and Lincoln counties in southwestern Wyoming. The towns of Pinedale, Boulder, Cora, and Daniel are located in the northern portion of the planning area; Big Piney and Marbleton in the central area; and La Barge in the southern portion. The planning area is located about 100 miles south of Yellowstone National Park. Teton and Bridger National Forests bound the planning area on the north and west, and Bridger National Forest and Bridger Wilderness area bound the area on the east. The Gros Ventre Range is north of the planning area, the Wind River Mountains are on the east, and the Wyoming and Hoback Ranges are on the west. The area varies in elevation from about 6,500 feet in the southwestern corner up to 9,500 feet along some of the mountain fronts. Mesas and buttes form the most common topographic features across most of the planning area. Most of the planning area lies within the Upper Green River and New Fork River watersheds, with an estimated 300 miles of stream and riverine habitat and 2,500 acres of lake and reservoir habitat supporting diverse wildlife populations. The dominant semiarid steppe climate is characterized by cold winters and short summers. Sagebrush and mountain shrub communities dominate the planning area, with some riparian-, saltbush-, and woodland-dominated areas. The diverse natural communities support a wide variety of game and nongame wildlife and fish species, including several Special Status Species. Hunting and fishing opportunities abound, and other types of recreational opportunities, such as river recreation, camping, and wildlife viewing, are also abundant. The planning area supports a variety of uses, including agriculture, recreation (including commercial outfitting), and, increasingly, oil and gas development. This chapter describes environmental characteristics, conditions, and trends that influence the resolution of planning issues or that would be affected by the management actions presented in Chapter 2. The status of the current environmental conditions is, in part, a result of the current Pinedale Resource Management Plan (RMP). Environmental components that would not be affected or that are not essential to the resolution of planning issues are not covered in detail. No new environmental data collection efforts were conducted on BLM-administered lands specifically for this RMP. Pinedale RMP 3-1 Chapter 3—Air Resources Final EIS 3.2 AIR RESOURCES 3.2.1 Climate The climate in the planning area is designated as Southern Rocky Mountain Steppe, a temperate semiarid steppe regime with average annual temperatures ranging from 35 to 45 degrees Fahrenheit (oF) (2 to 7 degrees centigrade [oC]) in most of the region, but reaching 50oF (10oC) in the lower valleys. The prevailing west winds and the general north-south orientation of the mountain ranges influence the climate. East slopes are much drier than west slopes; individual mountain ranges have similar east-west slope differences region-wide. Winter precipitation varies considerably with altitude. Total precipitation is moderate, but greater than on the plains to the east and west. In the highest mountains, a considerable part of annual precipitation is snow, although permanent snowfields and glaciers cover only relatively small areas. Bases of these mountains receive only 10 to 20 inches (260 to 510 millimeters [mm]) of rainfall per year. At higher elevations, annual precipitation increases to 40 inches (1,020 mm), and average temperatures fall (Bailey 1995). Weather stations are located in Pinedale (7,175 feet) and Big Piney (6,820 feet) in Sublette County, Wyoming. Meteorological data are available for Pinedale from August 1948 through April 2007 and for Big Piney from 1948 through 2006. Temperature Diurnal (morning to night) and seasonal (summer to winter) ranges in temperature are greater in valleys than on slopes (Martner 1986). Mean annual temperatures for Pinedale and Big Piney are 52oF and 53oF, respectively. Mean maximum summer temperatures of 75oF and 76oF and mean minimum winter temperatures of 0oF and 3oF occur in these two towns, respectively (Figures 3-1, 3-2, and 3-3) (Western Regional Climate Center). Precipitation High elevations experience greater amounts of precipitation than do lower elevations. The mean annual precipitation is 11 inches in Pinedale and 7.5 inches in Big Piney. The mean annual precipitation ranges from 5 inches in dry years to 19 inches in wet years in Pinedale. The mean annual precipitation in Big Piney ranges from 5 inches in dry years to 12 inches in wet years (Western Regional Climate Center). Figure 3-4 shows that mean monthly precipitation varies from 0.53 to 1.65 inches throughout the year in Pinedale and from 0.31 to 1.1 inches in Big Piney (Western Regional Climate Center). The mean total snowfall is 2 feet in Pinedale and 1 foot in Big Piney, with most snow occurring from November through April. Figure 3-5 shows that the mean monthly winter snowfall ranges from 6 to 12 inches in Pinedale and from 2 to 4 inches in Big Piney (Western Regional Climate Center). Trend data across three decades are shown monthly (Figures 3-6 and 3-7) and annually (Figure 3-8). These trends show a slight precipitation increase in Pinedale and a slight decrease in Big Piney (Western Regional Climate Center). Dispersion Atmospheric stability is a measure of the atmosphere’s capacity to disperse pollutants. Comprehensive wind measurements made closest to the planning area were collected in the Jonah Field Project Area adjacent to the southeast corner of the Pinedale Anticline Project Area (PAPA) at a meteorological station operated by BP from 1999 through 2003. Atmospheric stability class (Table 3-1 and Figure 3-9) is a measure of atmospheric turbulence, which directly affects pollutant dispersion. The stability classes are 3-2 Pinedale RMP Final EIS Chapter 3—Air Resources divided into six categories designated “A” (unstable) through “F” (very stable). The “D” (neutral) stability class occurs more than half of the time. The frequency and strength of winds greatly affect the transport and dispersion of air pollutants. Because of the strong winds in the region, the potential for atmospheric dispersion is relatively high, although nighttime cooling enhances stable air and inhibits air pollutant mixing and transport. Table 3-1. Atmospheric Stability Class Distribution Averaged from 1999 through 2003 Stability Class* Frequency (%) A 2.4 B 6.1 C 12.2 D 60.2 E 15.4 F 3.7 Source: BP 2004. * A = unstable; D = neutral; F = very stable Wind Direction and Velocity Wind speed and direction are highly variable as a result of the effect of local topography in the planning area. Comprehensive wind measurements made closest to the planning area were collected in the Jonah Field Project Area adjacent to the southeast corner of the PAPA at a meteorological station operated by BP from 1999 through 2003. Winds in the PAPA (Table 3-2) are from the west to northwest approximately 40% of the time. Table 3-2. Wind Direction Frequency Distribution in the Vicinity of the PAPA Averaged from 1999 through 2003 Wind Direction Frequency (%) N 5.3 NNE 3.9 NE 3.5 ENE 3.9 E 3.8 ESE 2.9 SSE 2.8 S 3.8 SSW 4.8 SW 6.6 W 9.9 WNW 15.9 NW 14.4 NNW 9.2 Source: BP 2004. While the annual mean wind speed is 11.2 miles per hour (mph), wind speeds in excess of 19 mph occur more than 12% of the time (Table 3-3). Pinedale RMP 3-3 Chapter 3—Air Resources Final EIS Table 3-3. Distribution of Wind Speeds in the Vicinity of the PAPA Averaged from 1999 through 2003 Wind Speed (mph) Frequency (%) 0–4.0 9.1 4.0–7.5 25.4 7.5–12.1 28.1 12.1–19.0 24.7 19.0–24.7 7.2 Greater than 24.7 5.5 Source: BP 2004. Figure 3-10 shows the occurrence frequency of wind speeds and wind directions for the Jonah Field in Wyoming. 3.2.2 Air Quality Characterization Elements of air quality addressed in the air quality analysis include concentrations of air pollutants, visibility, and atmospheric deposition. The air quality technical support document provides a summary of applicable air quality regulations (Appendix 19). 3.2.3 Ambient Air Quality Concentrations Ambient air concentration usually refers to the mass of pollutants present in a volume of air and can be reported in units of micrograms per cubic meter (µg/m3). Concentration can also be reported on a volume basis as parts per billion (ppb) and parts per million (ppm). The ambient air quality standards tables in Appendix 19 show both units for comparison. The Wyoming Department of Environmental Quality-Air Quality Division (WDEQ-AQD) determines background air quality levels. Because information collected from the nearest applicable monitoring stations indicates that current concentrations comply with applicable standards, air quality in the planning area is considered good. However, current and complete data on the concentrations of criteria air pollutants for the planning area are not available. The State of Wyoming has used monitoring to determine that the Pinedale region is in compliance with Wyoming Ambient Air Quality Standards (WAAQS) and the National Ambient Air Quality Standards (NAAQS). Table 3-4 shows ambient air concentrations of criteria air pollutants provided by the WDEQ-AQD. 3-4 Pinedale RMP Final EIS Chapter 3—Air Resources Table 3-4. Ambient Air Background Concentrations for Pinedale Measured Percent of Standards Data Pollutant/Averaging Background Data Source Time Measured Concentration NAAQS WAAQS (µg/m3) Carbon monoxide (CO) 1-hour 1,979 5 5 Data collected in Yellowstone National Park, Wyoming, at the monitoring site near “Old Faithful” during 8-hour 931 9 9 2005 (Pinedale Anticline Draft Supplemental Environmental Impact Statement [EIS] 2006).